The present invention relates to a cassette transfer mechanism for transferring a cassette containing a target object such as a semiconductor wafer or the like to be processed between a stand-by position where a cassette is set and a target transfer position where a target object is taken out from the cassette.
In general, to make various kinds of processing such as film formation processing, etching processing, or thermal oxidation processing on a semiconductor wafer or the like, a cassette including a number of wafers, e.g., twenty five wafers is contained in a cassette chamber. The wafers in the cassette thus contained in the cassette chamber are thereafter sent to a processing chamber through a transfer chamber by a transfer arm, under a vacuum atmosphere.
When a cassette is set in the cassette chamber, the cassette is set on a stage of the cassette chamber, with the wafer transfer port of the cassette oriented upwards. Thereafter, the cassette is taken into the cassette chamber while being rotated by about 90.degree. by a drive mechanism of a drawbridge type provided in the cassette chamber, and the wafer port is oriented in the horizontal direction from an upward direction.
In general, a plurality of cassette chambers, e.g., two cassette chambers are connected to one transfer chamber having one transfer arm. Therefore, in order that one transfer arm can make access with each of cassettes in two cassette chambers, each of the cassettes is oriented such that its wafer port once oriented in the horizontal direction faces in the moving direction of the transfer arm.
FIG. 12 shows a cluster tool apparatus which sends a semiconductor wafer W to a process chamber and makes processing on the wafer, by a series of operation as described above. This cluster tool apparatus mainly comprises two process chambers 2 and 4, a transfer chamber 6 connected to the process chambers 2 and 4, and two cassette chambers 8 and 10 connected to the transfer chamber 6. The chambers communicate with each other by gate valves G which can be closed air-tightly. As shown in FIG. 13, the transfer chamber 6 includes a transfer arm 12 of, for example, a multi-joint type which can be bent and rotated and transfers in and out semiconductor wafers W contained in cassettes C in the cassette chambers 8 and 10.
Due to the structure of the entire system and other conditions, each of cassettes C must be set on a stage outside the gate doors G1 of cassette chambers 8 and 10, such that the cassette C itself faces in the X-axis direction and such that its wafer port 14 is oriented upwards (in the Z-axis direction). Therefore, in order to take in cassettes C into cassette chambers 8 and 10 and to take out semiconductor wafers W from the cassettes C in the two cassette chambers 8 and 10, by one transfer arm 12, the cassettes C must be rotated in the horizontal direction while vertically raising up the cassettes C, thereby to orient the wafer ports 14 in the center direction (or the moving direction A) of the transfer arm 12.
Apparatuses which carry out an operation as described above are disclosed in, for example, U.S. Pat. No. 5186594, U.S. Pat. No. 5507614, and the like. In the U.S. Pat. No. 5186594, a cassette C set on a stage outside a cassette chamber 8 with its wafer transfer port 14 kept upwards is rotated by 90.degree. around the Y-axis in the figure by a drawbridge type drive mechanism, to be taken into a cassette chamber 8, and the wafer transfer port 14 facing upwards (in the Z-axis direction) is oriented to the horizontal direction (in the X-axis direction). In the next, the cassette C is rotated by a predetermined angle .theta. around the Z-axis in the figure, by a pivot mechanism, thereby to orient the wafer transfer port 14 to the center of an arm 12 (ref. FIG. 14). In addition, in U.S. Pat. No. 5507614, a cassette C is situated at a predetermined position and the wafer transfer port 14 is oriented to the center of the arm 12, at a breath, by rotating the inclination axis directed at a predetermined angle with respect to the gravity direction.
Meanwhile, since the apparatus of U.S. Pat. No. 5186594 requires a pivot mechanism in addition to a drive mechanism of a drawbridge type, i.e., since a drive mechanism for rotating a cassette C by 90.degree. around the Y-axis and a drive mechanism for rotating the cassette C by a predetermined angle around the Z-axis are individually required, the number of drive mechanisms in a vacuum chamber must be increased and the drive mechanisms must be complicated, resulting in that the manufacture costs are increased and the amount of particles thereby generated is also increased. The apparatus of U.S. Pat. No. 5507614 has a structure in which a rotation shaft extending obliquely is rotated and driven. Therefore, the rotation mechanism of this apparatus includes a larger deviated portion in comparison with a mechanism adopting horizontal rotation and driving, and accordingly, the amount of particles generated is increased. In addition, since a cassette C is rotated in an oblique direction, the space required for rotation is enlarged and the chamber has a large size.